/*
 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 *
 *
 */
package java.awt.dnd;

import java.awt.AWTEventMulticaster;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.util.EventListener;


/**
 * A class extends <code>AWTEventMulticaster</code> to implement efficient and
 * thread-safe multi-cast event dispatching for the drag-and-drop events defined
 * in the java.awt.dnd package.
 *
 * @see AWTEventMulticaster
 * @since 1.4
 */

class DnDEventMulticaster extends AWTEventMulticaster
    implements DragSourceListener, DragSourceMotionListener {

  /**
   * Creates an event multicaster instance which chains listener-a
   * with listener-b. Input parameters <code>a</code> and <code>b</code>
   * should not be <code>null</code>, though implementations may vary in
   * choosing whether or not to throw <code>NullPointerException</code>
   * in that case.
   *
   * @param a listener-a
   * @param b listener-b
   */
  protected DnDEventMulticaster(EventListener a, EventListener b) {
    super(a, b);
  }

  /**
   * Handles the <code>DragSourceDragEvent</code> by invoking
   * <code>dragEnter</code> on listener-a and listener-b.
   *
   * @param dsde the <code>DragSourceDragEvent</code>
   */
  public void dragEnter(DragSourceDragEvent dsde) {
    ((DragSourceListener) a).dragEnter(dsde);
    ((DragSourceListener) b).dragEnter(dsde);
  }

  /**
   * Handles the <code>DragSourceDragEvent</code> by invoking
   * <code>dragOver</code> on listener-a and listener-b.
   *
   * @param dsde the <code>DragSourceDragEvent</code>
   */
  public void dragOver(DragSourceDragEvent dsde) {
    ((DragSourceListener) a).dragOver(dsde);
    ((DragSourceListener) b).dragOver(dsde);
  }

  /**
   * Handles the <code>DragSourceDragEvent</code> by invoking
   * <code>dropActionChanged</code> on listener-a and listener-b.
   *
   * @param dsde the <code>DragSourceDragEvent</code>
   */
  public void dropActionChanged(DragSourceDragEvent dsde) {
    ((DragSourceListener) a).dropActionChanged(dsde);
    ((DragSourceListener) b).dropActionChanged(dsde);
  }

  /**
   * Handles the <code>DragSourceEvent</code> by invoking
   * <code>dragExit</code> on listener-a and listener-b.
   *
   * @param dse the <code>DragSourceEvent</code>
   */
  public void dragExit(DragSourceEvent dse) {
    ((DragSourceListener) a).dragExit(dse);
    ((DragSourceListener) b).dragExit(dse);
  }

  /**
   * Handles the <code>DragSourceDropEvent</code> by invoking
   * <code>dragDropEnd</code> on listener-a and listener-b.
   *
   * @param dsde the <code>DragSourceDropEvent</code>
   */
  public void dragDropEnd(DragSourceDropEvent dsde) {
    ((DragSourceListener) a).dragDropEnd(dsde);
    ((DragSourceListener) b).dragDropEnd(dsde);
  }

  /**
   * Handles the <code>DragSourceDragEvent</code> by invoking
   * <code>dragMouseMoved</code> on listener-a and listener-b.
   *
   * @param dsde the <code>DragSourceDragEvent</code>
   */
  public void dragMouseMoved(DragSourceDragEvent dsde) {
    ((DragSourceMotionListener) a).dragMouseMoved(dsde);
    ((DragSourceMotionListener) b).dragMouseMoved(dsde);
  }

  /**
   * Adds drag-source-listener-a with drag-source-listener-b and
   * returns the resulting multicast listener.
   *
   * @param a drag-source-listener-a
   * @param b drag-source-listener-b
   */
  public static DragSourceListener add(DragSourceListener a,
      DragSourceListener b) {
    return (DragSourceListener) addInternal(a, b);
  }

  /**
   * Adds drag-source-motion-listener-a with drag-source-motion-listener-b and
   * returns the resulting multicast listener.
   *
   * @param a drag-source-motion-listener-a
   * @param b drag-source-motion-listener-b
   */
  public static DragSourceMotionListener add(DragSourceMotionListener a,
      DragSourceMotionListener b) {
    return (DragSourceMotionListener) addInternal(a, b);
  }

  /**
   * Removes the old drag-source-listener from drag-source-listener-l
   * and returns the resulting multicast listener.
   *
   * @param l drag-source-listener-l
   * @param oldl the drag-source-listener being removed
   */
  public static DragSourceListener remove(DragSourceListener l,
      DragSourceListener oldl) {
    return (DragSourceListener) removeInternal(l, oldl);
  }

  /**
   * Removes the old drag-source-motion-listener from
   * drag-source-motion-listener-l and returns the resulting multicast
   * listener.
   *
   * @param l drag-source-motion-listener-l
   * @param ol the drag-source-motion-listener being removed
   */
  public static DragSourceMotionListener remove(DragSourceMotionListener l,
      DragSourceMotionListener ol) {
    return (DragSourceMotionListener) removeInternal(l, ol);
  }

  /**
   * Returns the resulting multicast listener from adding listener-a
   * and listener-b together.
   * If listener-a is null, it returns listener-b;
   * If listener-b is null, it returns listener-a
   * If neither are null, then it creates and returns
   * a new AWTEventMulticaster instance which chains a with b.
   *
   * @param a event listener-a
   * @param b event listener-b
   */
  protected static EventListener addInternal(EventListener a, EventListener b) {
    if (a == null) {
      return b;
    }
    if (b == null) {
      return a;
    }
    return new DnDEventMulticaster(a, b);
  }

  /**
   * Removes a listener from this multicaster and returns the
   * resulting multicast listener.
   *
   * @param oldl the listener to be removed
   */
  protected EventListener remove(EventListener oldl) {
    if (oldl == a) {
      return b;
    }
    if (oldl == b) {
      return a;
    }
    EventListener a2 = removeInternal(a, oldl);
    EventListener b2 = removeInternal(b, oldl);
    if (a2 == a && b2 == b) {
      return this;        // it's not here
    }
    return addInternal(a2, b2);
  }

  /**
   * Returns the resulting multicast listener after removing the
   * old listener from listener-l.
   * If listener-l equals the old listener OR listener-l is null,
   * returns null.
   * Else if listener-l is an instance of AWTEventMulticaster,
   * then it removes the old listener from it.
   * Else, returns listener l.
   *
   * @param l the listener being removed from
   * @param oldl the listener being removed
   */
  protected static EventListener removeInternal(EventListener l, EventListener oldl) {
    if (l == oldl || l == null) {
      return null;
    } else if (l instanceof DnDEventMulticaster) {
      return ((DnDEventMulticaster) l).remove(oldl);
    } else {
      return l;           // it's not here
    }
  }

  protected static void save(ObjectOutputStream s, String k, EventListener l)
      throws IOException {
    AWTEventMulticaster.save(s, k, l);
  }
}
